Washpipe stabilization system

ABSTRACT

The invention relates to washpipe assemblies for use in well bores and provides a washpipe assembly ( 2 ) comprising a washover shoe ( 10 ) attached to a washpipe ( 18 ), wherein a washpipe stabiliser ( 22 ) is provided on the washpipe ( 18 ) so that, when in use, deflection of the washover shoe ( 10 ) from a desired position is substantially prevented. The washpipe assembly of the present invention has the advantage over the prior art assemblies of providing means for supporting the washpipe off the wall of a well bore or well bore casing ( 52 ), and thereby reducing the torque required to rotate the washover string and the tendency of the washover shoe ( 10 ) to deviate from its preferred path down the well bore.

[0001] The invention relates to washpipe assemblies for use in wellbores.

[0002] It is common in the oil and gas drilling industry for equipmentto become trapped in a well bore so that access to the region of wellbore downhole of the equipment is restricted or prevented. Equipmentbecomes trapped for a variety of reasons. For example, sediment maysettle about the equipment, the formation surrounding the equipment maycollapse or the equipment may even be deliberately cemented. In order toremove equipment trapped under these circumstances, it is necessary toremove the external material retaining the equipment within the wellbore. It is well known that this may be achieved by means of a washoverstring. This type of string cuts the external material from the trappedequipment and transfers the cut material to the surface by means of wellbore fluid flow passing uphole through the annulus.

[0003] A conventional washover string typically incorporates a washovershoe, a washpipe, a drive sub (collectively referred to as the washpipeassembly) and a drive shaft linking the drive sub to drive equipmentlocated at the surface. The washover shoe is rigidly connected to thewashpipe and has the function of cutting the external materialpreventing the trapped equipment from being removed. Cutting elements,such as tungsten inserts, are provided for this purpose. Both thewashover shoe and the washpipe are typically of a cylindrical shapehaving large inner and outer diameters. The large inner diameters definea bore which is capable of receiving the trapped equipment as thewashover shoe cuts through the external material and moves downhole. Thewashpipe is rigidly connected to the drive sub which provides aconnection between the washpipe and the drive shaft. The washover stringis rotated by means of the drive equipment located at the surface and ispressed onto the external material until sufficient material has beencut to release the trapped equipment.

[0004] In order to guide the movement of the washover string as thewashover shoe cuts through the external material, stabilising means isgenerally provided on the drive shaft. The centralisation of thewashover shoe within the well bore is critical to the efficient andeffective use of a washover string. However, centralisation of thewashover shoe is often hindered when the direction of travel of thewashover string is capable of being influenced by the external profileof the trapped equipment. In these circumstances, the portion of thewashover string below the stabilising means tends to bend allowing thewashover shoe to deviate from its preferred course.

[0005] It is an objection of the present invention to provide a washpipeassembly which does not tend to deviate from its preferred course whenthe washover shoe engages the trapped equipment to be washed over.

[0006] The present invention provides a washpipe assembly for use in awell bore, the washpipe assembly comprising a washover shoe attached toa washpipe, wherein a washpipe stabiliser is provided on the washpipe sothat, when in use, deflection of the washover shoe from a desiredposition is substantially prevented.

[0007] The distance between the stabiliser and washover shoe in thewashpipe assembly of the present invention is considerably less than intraditional washpipe assemblies. The close proximity of the stabiliserto the washover shoe reduces the degree of bend in the washover stringbetween the washover shoe and the stabiliser. Consequently, the tendencyof the washover shoe to deviate from the preferred path down the wellbore is reduced.

[0008] It is preferable for the washover shoe to be a cylinder defininga bore, the cylinder of the washover shoe being provided with cuttingmembers located on the lower end portion thereof. Furthermore, it isdesirable for the bore of the washover shoe to be adapted to receiveequipment located within the well bore. Thus, as the washover shoe cutsexternal material surrounding trapped equipment and subsequentlyprogresses down the well bore, the trapped equipment may be receivedwithin the washover shoe bore.

[0009] The washpipe of the present invention may be provided as anelongate cylinder defining a bore. Preferably, the bore of the washpipeis adapted to receive equipment located within the well bore. Thus,trapped equipment received by the bore of the washover shoe may progressinto the bore of the washpipe as further external material is cut andthe washover string moves further downhole.

[0010] The stabiliser is preferably provided as a plurality of blademembers projecting from an exterior surface of the washpipe. Thestabiliser preferably incorporates five blade members and each blademember is preferably arranged in a helix about the washpipe.Furthermore, each blade member is preferably provided with a cuttingedge. It is also desirable for the stabiliser to be provided on aportion of the washpipe adjacent the washover shoe.

[0011] The washpipe assembly of the present invention has the advantageover the prior art assemblies of providing means for supporting thewashpipe off the wall of the well bore or well bore casing, and therebyreducing the torque required to rotate the washover string and thetendency of the washover shoe to deviate from its preferred path downthe well bore.

[0012] A specific embodiment of the present invention will now bedescribed with reference to the accompanying drawings, in which:

[0013]FIG. 1 is a cross-section view of a washpipe assembly according tothe present invention;

[0014]FIG. 2 is a side view of the stabiliser shown in FIG. 1;

[0015]FIG. 3 is an end view of the stabiliser shown in FIG. 2; and

[0016]FIG. 4 is a cross-section view of the washpipe assembly of FIG. 1located within a well bore above trapped equipment.

[0017] The washpipe assembly 2 shown in FIG. 1 incorporates a number ofcomponents rigidly attached to one another by means of threadedconnections 4, 6, 8. The components include a washover shoe 10, a lowerwashpipe 12, an upper washpipe 14 and a drive sub 16. The lower washpipe12 is rigidly attached to the upper washpipe 14 by means of threadedconnection 6 and thereby provides a complete washpipe 18 of the desiredlength. The lower end of the washpipe 18 is rigidly attached to thewashover shoe 10 by means of threaded connection 4. The upper end of thewashpipe 18 is rigidly attached to the drive sub 16 by means of threadedconnection 8. When in use, the drive sub 16 is threadedly connected to adrive shaft 20 (shown in FIG. 4).

[0018] The washpipe 18 is provided with a stabiliser 22 incorporatingfive blade members 24 arranged in a helix about the lower washpipe 12.The blade members 24 are formed as an integral part of the lowerwashpipe 12 and may be provided by machining, welding or any othersuitable manufacturing techniques. A detailed view of the washpipe 18 isprovided by FIGS. 2 and 3. The washpipe assembly 2 has dimensionssuitable for a 9.625 inch well bore casing having an inner diameter of8.681 inches. The outer diameter 26 of the washpipe is 8.125 inches andthe outer diameter 28 of the blade members 24 is 8.500 inches. Thewashpipe 18 defines a washpipe bore 30 having a diameter 32 of 7.285inches. The bore 30 and the length of the washpipe 18 are of sufficientmagnitude to receive trapped equipment when the washpipe assembly 2 isin use. An appropriate length of washpipe 18 may be arranged prior touse by selecting suitable lengths of lower and upper washpipe sections12, 14 or by using a suitable number of standard length washpipesections. Each blade member 24 of the stabiliser 22 has a helix angle 34of 5.2° and has a width 36 at 90° to the helix of 2.625 inches.Furthermore, each blade member 24 is provided with a cutting edge 25.

[0019] The washover shoe 10 has substantially the same outer diameter asthe washpipe 18 and is provided with a bore 38 having substantially thesame diameter as the washpipe bore 30. The bores 30, 38 of the washpipe18 and the washover shoe 10 are in fluid communication with one anotherand with a bore 40 provided in the drive sub 16. When in use, the bores30, 38, 40 of the washpipe assembly 2 are in fluid communication withthe surface via a bore 42 provided in the drive shaft 20 (see FIG. 4).

[0020] The lower end portion 44 of the washover shoe 10 has a smallerinternal diameter and a larger external diameter than the main body ofthe washover shoe 10. Tungsten inserts (not shown) are provided on theexternal surface 46, the lower surface 48 and the internal surface 50 ofthe lower end portion 44 so as to provide means for cutting externalmaterial from equipment trapped within a well bore. The lower endportion 44 has an external diameter equal in magnitude to that of theouter diameter 28 of the blade members 24. The external diameter of thelower end portion 44 may alternatively have a greater magnitude than theouter diameter 28, but should not have a magnitude less than the outerdiameter 28 since this would prevent the passage of the stabiliser 22passed the trapped equipment during the washover operation. The lowersurface 48 of the washover shoe 10 is provided with fluid courses (notshown) which allow the flow of well bore fluid passed the externalmaterial being cut, thereby cooling the washover shoe 10 and removingcut portions of the external material.

[0021] The washover operation of the washpipe assembly 2 is shown inFIG. 4 of the accompanying drawings. The washpipe assembly 2 is attachedto a drive shaft 20 and run down a well bore 52 until the washover shoe10 abuts external material 54 preventing removal of trapped equipment56. The external material 54 is removed by rotating the drive shaft 20and the washpipe assembly 2 by means of the drive equipment located atthe surface. External material 54 cut from the trapped equipment 56 isremoved by a flow of well bore fluid passing downhole through the bores42, 40, 30, 38 of the washover string, through the fluid courses anduphole through the annulus 58. The direction of flow of the well borefluid is indicated by arrows A, B and C.

[0022] As the washover shoe 10 cuts away the external material 54, thewashover string is pushed downhole. As the washover shoe 10 progressesdown the well bore 52, the trapped equipment 56 is received within thebores 38, 30 of the washover shoe 10 and the washpipe 18. The tendencyof the washover shoe 10 to be deflected from a central position withinthe well bore 52 is reduced by the guiding effect of the stabiliser 22.The washpipe assembly 2 is moved down the well bore 52 so that thewashover shoe 10 cuts away the external material 54 located both abovethe trapped equipment 56 and between the trapped equipment 56 and thewell bore 52. Movement of the washpipe assembly 2 down the well bore 52is continued until the stabiliser 22 passes the trapped equipment 56.The blade members 24 of the stabiliser 22 not only guide the washovershoe 10, but also act as a milling tool and clean the interior surfaceof the well bore 52 in the region of the trapped equipment 56.

[0023] The present invention is not limited to the specific embodimentdescribed above. Alternative arrangements and suitable materials will beapparent to a reader skilled in the art.

1. A washpipe assembly for use in a well bore, the washpipe assemblycomprising a washover shoe attached to a washpipe, wherein the washpipestabiliser is provided on the washpipe so that, when in use, deflectionof the washover shoe from a desired position is substantially prevented.2. A washpipe assembly as claimed in claim 1 , wherein the washover shoeis a cylinder defining a bore, the cylinder of the washover shoe beingprovided with cutting members mounted on the lower end portion thereof.3. A washpipe assembly as claimed in claim 2 , wherein the bore of thewashover shoe is adapted to receive equipment located within the wellbore.
 4. A washpipe assembly as claimed in any of the preceding claims,wherein the washpipe is an elongate cylinder defining a bore.
 5. Awashpipe assembly as claimed in claim 4 , wherein the bore of thewashpipe is adapted to received equipment located within the well bore.6. A washpipe assembly as claimed in any of the preceding claims,wherein the stabiliser is provided as a plurality of blade membersprojecting from an exterior surface of the washpipe.
 7. A washpipeassembly as claimed in claim 6 , wherein each blade member is arrangedin a helix about the washpipe.
 8. A washpipe assembly as claimed inclaim 6 or 7 , wherein the stabiliser incorporates five blade members.9. A washpipe assembly as claimed in any of claims 6 to 8 , wherein theblade members are provided with a cutting edge.
 10. A washpipe assemblyas claimed in any of the preceding claims, wherein the stabiliser isprovided on a portion of the washpipe adjacent the washover shoe.
 11. Awashpipe assembly substantially as hereinbefore described with referenceto, and as shown in, the accompanying drawings.